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Ethylmalonic Acid.—Like acetoacetic ester (see p. 83),
dlethylmalonate contains the group CO.CHo.CO. By the
action of sodium or sodium alcoholate, the hydrogen atoms of
the methylene group are successively replaceable by sodium.
The sodium atoms are in turn replaceable by alkyl or acyl
groups. Thus, in the present preparation, ethyl malonic ester
is obtained by the action of ethyl iodide on the monosodium
compound. If this substance be treated with a second mole-
cule of sodium alcoholate and a second molecule of alkyl iodide,
a second radical would be introduced, and a compound formed
of the general formula
in which X and Y denote the same or different radicals.
These compounds yield, on hydrolysis, the free acids, which,
like all acids containing two carboxyl groups attached to the
same carbon atom, lose CO2 on heating. Thus, ethyl malonic
acid yields butyric acid. In this way the synthesis of mono-
basic acids may be readily effected. Malonic ester, moreover,
may be used in the preparation of cyclic compounds as well as
of tetrabasic and also dibasic acids of the malonic acid series
(Perkin). To give one illustration : malonic ester, and ethylene
bromide in presence of sodium alcoholate, yield trimethylene
dicarboxylic ester and tetramethylene tetracarboxylic ester. Th e
first reaction takes place in two steps,
CHNa(COOC3HB)2 + CaH4Br3 = CHoBr.CH.,CH(COOC2H5)2 + NaBr.
CH.,' "
= |    " >C(COOC,H5)o + NaBr + CH,(COOC,H5).,.
In the second step a second molecule of sodium malonic ester
exchanges its sodium -with the substituted malonic ester and a
second molecule of NaBr is then removed.
The formation of the tetracarboxylic ester occurs simultane-
2CHNa(COOCoH,)., + G,H4Br.,
= (COOCoH5).2CH. CH2. CH,. CH(COOCaH6)2 + 2NaBr